JPH01274152A - Exposure device - Google Patents

Abstract

PURPOSE:To maintain waveform at a specific value at all times without hastening the consumption of components and gas by oscillating pulse light before the time when variation in the wavelength exceeds a specific range is elapsed in a nonexposure state, and detecting and controlling the wavelength. CONSTITUTION:This exposure device is equipped with the resonator mirrors 1 and 2 of an excimer laser, etalons 3 and 4, a gas chamber 5, a wavelength monitor 12, an exposure control part 10, a wavelength controller 11, a 1st lighting optical system 7, a 2nd lighting system 9, a reticle R, a projection lens L, and a wafer W. Then the pulse light is oscillated intermittently by a light source before the time when the variation in the previously measured wavelength of the pulse light exceeds the constant range is elapsed except in the irradiation period of light to an object, thereby controlling the wavelength to a specific value. Namely, a wavelength detecting means 12 detects the wavelength of the pulse light and the wavelength is controlled to the specific value according to its detection signal. Consequently, a shift in the center of a spectrum due to the thermal deformation, etc., of an optical element during the nonexposure state is prevented to maintain the wavelength at the specific value at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure apparatus using an excimer laser or the like as a light source used in the manufacture of integrated circuits.

[Prior Art] Exposure equipment in the deep UV range that uses an excimer laser such as krypton fluoride (KrF) as a light source has the potential to become the main equipment in lithography processes that form patterns of 0.5 μm or less. This type of exposure equipment is attracting attention as having a strong oscillation, and in particular uses only quartz, which has a high transmittance, as the optical material for the projection lens, and uses the excimer laser as a light source by narrowing the oscillation spectrum width of the excimer laser compared to its natural oscillation state. Early commercialization is expected.

In such an exposure apparatus, a dispersive element such as an etalon, a prism, or a grating is arranged as a wavelength selection means in the resonator of the excimer laser light source, and the center of the oscillated spectrum is determined by the wavelength selection of the dispersive element placed inside the resonator. Determined by gender. Additionally, if the projection lens is made of quartz only, chromatic aberration will occur and the aberration can only be corrected for a specific spectrum, so if the center of the oscillation spectrum shifts from a specific setting value to outside a limited range, the projection magnification will change. or out of focus. That is, in such an exposure apparatus, it is important to stabilize the center of the oscillation spectrum.

Conventionally, wavelength control in this type of exposure equipment is performed by detecting the wavelength of pulsed light and based on this detection signal, so in order to stabilize the wavelength, even during periods when the target is not irradiated with light, It is desirable to continue oscillating pulsed light in the same way as during exposure.

[Problem to be solved by the invention] However, the lifespan of parts such as the gas inside the excimer laser resonator, the window that separates the inside and outside, other spectroscopic elements (etalon, busosm, etc.), and electric elements depends on the number of oscillation pulses. Therefore, it is not practical to always oscillate the excimer laser in the same way as during exposure as described above.

In other words, these consumables and parts expire quickly and must be replaced or cleaned in short cycles, which increases running costs and requires frequent shutdowns of the exposure equipment for replacement. The throughput also decreases.

The present invention has been made in view of these points, and it is an object of the present invention to provide an exposure apparatus that can always maintain the center of the oscillation spectrum at a predetermined value without accelerating the wear and tear of components.

[Means for Solving the Problems] In the present invention, the light source is turned off before a predetermined time period has elapsed in which the previously measured wavelength change of the pulsed light exceeds a certain range during a period other than the light irradiation period to the target object. The above problem has been achieved by intermittently oscillating pulsed light from the source and controlling the wavelength to a predetermined value.

[Function] In the present invention, the light source intermittently oscillates pulsed light before a predetermined time period has elapsed during which the wavelength change of the pulsed light exceeds a certain range during a period in which the target object is not irradiated with light. The wavelength of this pulsed light is detected by a wavelength detection means,
The wavelength can be controlled to a predetermined value based on the detection signal. Therefore, it is possible to prevent the center of the spectrum from shifting due to thermal deformation of the optical element during non-exposure, and to maintain the wavelength at a predetermined value at all times.

Here, the time period during which the wavelength change of the pulsed light exceeds a certain range is a value determined depending on the configuration of the light source, and is measured in advance and stored in the exposure control section or the like.

Since this time is usually about several minutes, the oscillation frequency of the pulsed light during non-exposure is more than two orders of magnitude lower than the frequency during exposure. Therefore, there is almost no wear and tear on gas inside the resonator, spectroscopic elements, discharge electrodes, switching elements, and other parts due to oscillation during non-exposure. In this way, the present invention can always maintain the center of the spectrum at a predetermined value without accelerating the wear of parts, and can promptly irradiate light of a predetermined wavelength during exposure.

The oscillation of the pulsed light during non-exposure may be performed before the wavelength changes or exceeds a certain range, as described above, and does not necessarily have to be periodic.

[Example] FIG. 1 is a block diagram showing an embodiment of the present invention.

1.2 is the resonator mirror of the excimer laser, which includes an etalon 3゜4 to narrow the spectrum width and a gas chamber (with a discharge part rL) for exciting the excimer laser.
A tube) 5 is interposed between them. The wavelength of the beam B emitted from the excimer laser light source is within the spectral width determined by the gain of the excimer laser, and is ultimately determined by the wavelength selectivity determined by the angle of the etalons 3 and 4 with respect to the beam B.

A portion of the beam B extracted from the excimer laser light source is reflected by the beam splitter 6, and the reflected beam B is guided to the wavelength monitor 12. The wavelength monitor 12 has a function of determining the deviation of the oscillation wavelength from a predetermined wavelength,
Wavelength control device 1 controlled by a signal from exposure control section 10
Outputs the wavelength deviation to 1. The wavelength control device 11 then controls the wavelength by changing the angle of the etalon 3 or 4 by a predetermined amount in accordance with the input deviation.

On the other hand, the beam that has passed through the beam splitter 6 enters a first illumination optical system 7 that is controlled by an exposure control section 10.

The first illumination optical system 7 includes a variable attenuator that attenuates the intensity of the beam at a predetermined attenuation rate, and also has functions for making the intensity distribution uniform and expanding the beam size. Then the first
The beam exiting the illumination optical system 7 is reflected by a reflection mirror 8 and then transferred to a second illumination system (including a main condenser lens, etc.) 9
The top of the reticle R is illuminated through. Then, the pattern formed on the lower part of the reticle R is reduced in size and projected onto the wafer W by a projection lens.

Here, the wafer W is automatically transported by a wafer loader 13 operated by a signal from the exposure control section 10, and is set on and removed from the wafer holder WH without manual intervention. In addition, the wafer W is moved two-dimensionally (XY) by the wafer stage WS while being attracted to the wafer holder WH.
The wafer stage WS is moved in the direction and the height (Z) direction, and for one wafer W, a step-and-repeat operation is performed after the alignment operation, that is, the movement of the wafer stage WS and the repetition of exposure are performed.

FIG. 2 is a time chart of excimer laser emission.

First, in the exposure state T1, a plurality of pulsed lights (e+ and e2) are oscillated at the highest repetition frequency of the excimer laser light source every time the wafer stage WS moves, and a predetermined area of the wafer W is exposed. When all shot areas of one wafer W have been exposed, the wafer W is replaced with the next wafer W and a sequence such as alignment begins. In the figure, this non-exposure period (idling period) is indicated by I, but in this embodiment, the light source oscillates pulsed light before the time period during which the wavelength change exceeds a predetermined range has elapsed. That is, idling oscillation is performed at a repetition frequency lower than that during exposure. For example, if the oscillation frequency during exposure is 200 to 500 Hz, the frequency during idling oscillation may be about 1 to 211 z, and at this frequency there is almost no wear on optical members, etc. Note that during such idling oscillation, it is necessary to block the oscillated pulsed light by operating a shutter provided at an appropriate position in the optical path so that the oscillated pulsed light does not reach the wafer W undergoing alignment or waiting.

Subsequently, when the next wafer W enters the exposure state T2, each area is exposed by a group of pulsed light of f+, fz, f3..., but the wavelength is changed using the light emission pulse at I during idling. Since it is constantly controlled, there is no wavelength error at the start of exposure, allowing for highly accurate exposure. Also,
In the exposure state T2, there are a large number of light emission pulses, so by detecting this wavelength, wavelength control can be performed without any problem.

In addition, in the present invention, the pulsed light oscillated during non-exposure can be used not only for wavelength control but also for output energy control, thereby making it possible to stabilize the output energy. In addition, if any abnormality is discovered during oscillation during non-exposure, the cause of the abnormality can be investigated and appropriate measures taken before the wafer is exposed, which improves the operating rate of the exposure equipment and It is possible to prevent defects from occurring.

[Effects of the Invention] As described above, according to the present invention, during non-exposure, pulsed light is oscillated before the wavelength change exceeds a predetermined range, and this wavelength is detected to control the wavelength. As a result, the wavelength can always be maintained at a predetermined value without accelerating the consumption of parts or gas. Therefore, if such an exposure apparatus is used, there will be no wavelength error at the start of exposure, and extremely good imaging characteristics of the projection lens can be stably obtained. Furthermore, since there is no waiting time until wavelength control is normally performed at the start of exposure, throughput is also improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a time chart showing the light emission state of the embodiment shown in FIG. [Explanation of symbols of main parts] 1.2... Excimer laser resonator mirror 3.4.!・
Etalon 11...Wavelength control device 12...Wavelength detection means R...Reticle...Projection lens W...Wafer agent Patent attorney Masatoshi Sato

Claims (1)

[Claims] In an exposure apparatus that has a wavelength detection means for detecting the wavelength of pulsed light emitted from a light source, controls the wavelength to a predetermined value based on the detection signal, and irradiates a target with light of a substantially constant wavelength. , intermittently oscillating pulsed light from the light source during a period other than the period of light irradiation to the target object, before a predetermined time period has elapsed in which the wavelength change of the pulsed light measured in advance exceeds a certain range; An exposure apparatus characterized in that the wavelength is controlled to a predetermined value.